1. Field of the Invention
The present invention relates to a magnetic head which is appropriate for recording to and reproducing from a high coercive force magnetic recording medium such as a so-called metal tape, and which has a high saturation flux density metal disposed near the magnetic gap of ferrite cores comprising part of the magnetic head.
2. Description of the Prior Art
Recently, in video tape recorders and digital tape recorders, techniques to achieve short wavelength recording and to increase track density have been remarkably developed so as to reduce tape sizes and to accomplish high quality image or audio recording. As a result, so-called metal tapes which have high coercive forces are becoming important.
To perform recording to or reproducing from such metal tapes, core materials of a high saturation flux density are required: conventional bulk-type Sendust heads are insufficient because not enough reproduction efficiency is too low owing to their eddy current losses. The latest technical progress in the field of magnetic heads, however, makes it possible to implement so called metal-in-gap heads which have magnetic films of a high saturation flux density metal such as Sendust disposed on the magnetic-gap-formed surfaces of ferrite cores of the magnetic heads. This enables the recording performance and reproduction efficiency to be maintained at a high level.
FIG. 1 is a perspective view showing an example of a conventional metal-in-gap head which comprises ferrite cores 1a and 1b made from a single crystal ferrite of Mn-Zn, Sendust films 2a and 2b made of films of a high saturation flux density metal to cover the magnetic-gap-formed surface, and a nonmagnetic glass 3 filled between the ferrite cores 1a and 1b to define a track width (i.e., gap length). Here, the single crystal ferrite is used as follows: (110) planes are used as a tape sliding surface 4 (i.e., surfaces 4a and 4b) and a side surface 5 (i.e., surfaces 5a and 5b); that is, the notation (110) as used in this specification corresponds to the notation {110} for planes of equivalent symmetry. See, for example, Semiconductor Devices, Physics and Technology, pages 6 and 7, S.M. Sze, John Wiley & Sons (1985). The easy magnetization directions &lt;100&gt; in the sliding surface 4, that is, in the plane (110) is directed in parallel with the side surface 5, namely, in the lengthwise direction of the track as shown in FIG. 1.
The conventional metal-in-gap head, however, has a problem that distortions appear in the reproduced signals when signals including low frequency components are reproduced, and hence noise in the frequency spectra increases. This is because, in the metal-in-gap head, the ferrite cores are subjected to a stress strain which is produced by the difference in the physical characteristics of ferrite cores and magnetic metal films.
An example of this will be described with reference to FIGS. 2A and 2B. FIG. 2A shows a normally recorded and reproduced waveform 11 of a sinusoidal signal of 750 kHz. The same head, however, produces, at a certain probability, a waveform 12 which includes a parasitic wave portion 13 at a shoulder part thereof as shown in FIG. 2B. FIG. 3 shows frequency spectra of the signals shown in FIGS. 2A and 2B. In FIG. 3, the x axis represents the frequency of the reproduced signals, and the y axis represents the amplitude of the signals. As shown in FIG. 3, noise of the abnormal waveform 12 increases over the entire frequency region. This phenomenon is called "a wiggle phenomenon". No wiggle phenomenon is observed with a signal without a low frequency component.
The wiggle phenomenon presents the following problems: it will increase the noise components in reproduced signals of, for instance, video signals including color signals, thus decreasing the S/N ratios of images; or it will increase the error rate of digital signals including their low frequency components.